Unidirectional flow in plurality chamber induction furnace



3 Sheets-Sheet 1 F a g F i g. 4.

INVENTOR M 75m BY %ZWM ATTORNEY M. TAMA UNIDIRECTIONAL FLOW IN PLURALITYCHAMBER INDUCTION FURNACE Feb. 13, 1951 Filed June 20, 1947 Feb. 13,1951 M. TAMA 2,541,841

- UNIDIRECTIONAL FLOW IN PLURALITY CHAMBER INDUCTION FURNACE Filed June20, 1947 5 Sheets-Sheet 2 Feb. 13, 1951 M. TAMA UNIDIRECTIONAL FLOW INPLURALITY CHAMBER INDUCTION FURNACE 3 Sheets-Sheet 3 Filed June 20, 1947ATTORNEY Patented Feb. 13, 1951 UNITED STATES PATENT OFFICE UNIDIRECTIONAL FLOW IN PLURALITY CHAMBER INDUCTION FURNACE Mario Tama,Morrisville, Pa.,- assignor to Ajax Engineering. Corporation, Trenton,N. ..].v

Application .Iune2'0, 1947, SeriaI'N0. 7.55,,886

4 121Glaims.

This invention relates to an induction furnace and particularly to amulti-chamber induction furnace of the stationary and of the tiltabletype. These furnaces are generally provided with two ormore' metalholding chambers or hearths and these chambers (or hearths) areconnected by a system of channels or ducts forming the secondary meltingloop; the channels are in the customary manner threaded by primarytrans-.

former units.

The furnaces are frequently equipped with a rocking or rotating. device;the rocking of the furnace imparts to the molten metals an agitating andmixing action in order to equalize the metal charges held in the variouschambers or transmission of theheat which is inductively created by theprimary transformer unit or units to the metal charges in the variousholding chambers.

' Prior attempts to impart to induction furnaces an effective and fastdistribution of the inductively created heat to the molten metal chargeand to produce uniform metal melts have been based on the production ofa metal movement by the creation of temperature differences in thesecondary melting channels, which for thi purpose were equipped withsections of a smaller and a' larger cross-area; it was assumed that" ahigher temperature could be obtained in the places of smaller crosssection whereby aonedirectionalmetal flow would be initiated. However,these and other attempts to create a unidirectional flowor circulationof the molten metal chargeininduction furnaces have remainedentirelyunsuccessful.

-The' creation of a one-wayor unidirectional now of the metal is indeedhighly desirable in induction furnaces and particularly in those of thesubmerged resistor type and many suggestions have been continuously madein the source of the past forty years to satisfactorily solve thisproblem.

2 These suggestions include: 7 The provision of" a plurality of separateand of moving electromagnetic fields,

Of open loop reservoirs for" the charge and closed loop channelsconnecting with the reservoir at remotely separated places.

The arrangement of hearth entering ends of the loop at verticallydifferent levels,

The-gradual enlargement of the loop cross-area from one to the otherhearth entering points,

The co-axial arrangement" of the primary and the secondary and Thedisplacement from each other in an axial direction.

Some of the known constructions utilize the;

pinch-effect and some have been designed with the purpose to prevent thedisruption ofthe metal flow'by the latter.

The above recited numerous endeavors demonstrate the importance of asatisfactory flow control of the molten metal in induction furnaces; butnone of them has attained the status of practical usefulnessbecause theyare based on constructional changes of the secondary loop itself.

Even. if a unidirectional. pressure fiow'is shown in the prior art fromone outlet of'thesecondary' loop. through. the; charge into. another.outlet of thexloop and areturn flowthrough the latter, this flow is;on. account. of: the heavy weight: of the: superposed metalcharge-,necessarily confined tov its lower; portion; this; isparticularly true of' deep-chargeswhere the flow-impetus of the metal:emerging. from the. loop into. the hearth is. soon counteracted by theweight of. the charge;

As mentioned above, the movement of the at the emergence point. ofthemelting' channels into. the hearth effecting a direct return movementof the molten charge-into the same channels.

The metal flow produced by the pinch effect in a submerged resistor typeinduction furnace having a melting loop composed of a channelspaced:from the hearth and apl'ura'lity ofsubstantially straight channelsconnecting: the

spaced channel with the hearth is illustrated in attached Fig. 1',showing the meltingloop and the bottom section of the hearth.

Theelectromagnetic field of highest intensity is located inthe centersection of the straightmelting channels 5 at" about half their length.

The metal is formedfiom this center section at an upward and in adownward direction through the melting channels, as indicated by thearrows. The molten metal stream emerging from the ends of the channelsdraws the metal from adjacent portions of the charge into the samechannels, whereby two lateral fiow branches result which are againoutwardly forced as they approach the center portion of the channels.Under the direct influence of the electromagnetic, field the well knownflow of the melt in opposite directions results through the samechannel, as shown for instance in U. S. Patent Sasnett No. 1,660,209 andindicated by the arrows in Fig. 1.

Within the range of its highest intensity the electromagnetic field hasthe tendency to compress the molten conductor; if the current input issufficiently high, it may happen that the conductor is interrupted orpinched; thus the term pinch effect was created.

However, and as above stated, the direct return of the metal into themelting channel is the consequence of the metal pressure produced by theelectromagnetic field and the resulting sucking effect in coactlon withthe pressure distribution in melting channels; it will therefore nottake place in those portions or layers of a molten metal charge, whichare not influenced by the electromagnetic field.

The pressure distribution resulting in the adjacent sections $-.')3 andyy at the transition point of the metal from the channel mouth into thehearth is illustrated in Figs. 2 to 5.

The hydrostatic pressure HP which increases from the surface of the meltdownward is shown in Fig. 5; at the point a: it is HX, at the point 1 itis Hy.

The pinch effect produces a superimposed inwardly directed pressurewhich, as can be shown by simple calculation, increases on a paraboliccurve from the periphery of the channel toward its center, where thepressure attains its maximum. This pressure is wheregI denotes thecurrent and r the radius of theconductor.

TtIt'is obvious that the pressure maximum Py in the smaller section y-yis smaller than the pressure PX in the larger section r--r. The adjacentpoints a and b are consequently subjected to various pressures and, aswill appear from Fig. 4, the pressure at b is higher than that at 2,Fig. 3. This causes the liquid conductor to be squirted-out in thedirection b to a; the metal upwardly propelled in the direction of thecenter arrow is replaced by metal drawn back from adjacent portions ofthe charge, as shown by the lateral arrows in Figs. 1 and 2. A similarmetal'flow is produced at the emergence of. channels 5 into channel 6,Fig. 1.

This metal transport through the melting channels of the furnace has itsadvantages; it prevents, for instance, the overheating of the metal inthe melting channels. However, the non-controlled metal movement islocally limited and obviously insufficient to have a decided influenceon the equalization of the charge and the distribution of the heatthereto; moreover, the current input is limited and the high powerfactor required for the steadily increasing capacity of modern inductionfurnaces cannot be obtained because current increase involves the dangerof the conductor being interrupted in the zone of the highest fieldintensity. Some of the known suggestions to create a unidirectional flowalso involve difficulties in the construction of the furnace itself andgreatly raise its manufacturing costs.

It is therefore the primary object of this invention to create in amulti-chamber induction furnace an equalization of the metal melts inthe various chambers and'uniformity with regard to chemical compositionand temperature.

It is a further object of the invention to achieve this aim withoutrocking the furnace and without the application of rotatable devices,such as supporting rollers and the like.

It is another important object of the invention to create in thesefurnaces a continuous unidirectional closed metal flow through thevarious chambers with adherent uniformity of the metal in the same; thisis of particular importance in the mass-foundry and die-casting practiceof,

particularly, light metals where the production of uniform castings is adominant postulate which has hitherto not been satisfactorily met withinthe customary mechanically rocked induction furnaces.

It is a further object of the invention to permit a practicallyunlimited increase of the power factor or current density withoutincurring the. danger of interrupting the conductor or clogging.

the melting loop.

It is a further important object of the inven tion to successfully meltin these furnaces smallsizedmetal materials such as scrap, turnings,

borings, chippings and even fine metal powders.

It is a further Object of the invention to optionally increase the powerfactor of the furnace and to obtain with the same amount of iron in thetransformer a larger power input.

It is also an object of the invention to greatly reduce slag depositionin the melting loop and particularly in the center section of themelting channels as the continuous unidirectional metal flow through theentire channel length prevents the slag particles from coming to rest.

With the above recited and. other objects in.

in an opposite direction from the first chamber through the melting loopinto the other chamber.

In this manner, the molten metal is forced to, participate in acontinuous one-way or unidirec tional circulation through the variouschambers and a highly satisfactory equalization of the charge isobtained which is far superior to the rocking of the same, is far lessexpensive and is equally applicable to stationary and tiltable furnaces.

The inductively created heat is equally and uniformly distributedthroughout the entirecharge of the various chambers. Small-sized metalscrap and metal powders may be molten without difliculty, which hithertohas been unattainable in multi-chamber induction furnaces.

A simple means to obtain the above described closed and unidirectionalflow of the entire charge consists in the location of a currentconductive refractory tube, for instance, a graphite or carbon. tube in:a melting channel or directly above. its upper end. in. such. amannerthat. the tube forms an extension of the channel; the tube;

ends within. or above a section of the melt: which is practically freefrom the influence of the. in-.

ducedelectromagnetic. field- The invention-relates to an inductionfurnace ofthe submerged resistor type. as. disclosed. in

copending U patentv applications Serial No- 647,831, filed. Feb. 15,1946, now Patent No. 2,536,325,.v issued. Jan. 2,1951; Serial No-683,115.,

filed. July 12,, 1946, now Patent. No- 2,539,215,. issued. Jan..23,1951; Serial No. 671,818, file'dMay 23,. 1946, now Patent No.2,536,859, issued Jan. 2,. 1951.; and Serial No. 735,851, filed, Mar-20, 1947.

The invention is. basedon the general idea also inherent inthese.copending. patent applications.

oficreating, in the submerged resistor type furnace a unidirectionalmetal flow from. the melting loop into a zone which is essentially free.from inductive influence;,for this: purpose a, refractory tube isinserted. with; its one end into the melting: loop; the tube reaches;with. its other end into a. zone. which. is essentially not influencedby inducmetal froman induction furnace by inserting av refractory,current-conductive tube into a meltingchannel; certain claims. includethe maintenanceof a small clearance between the. outside of the.inserted tube and the inside of the melting duct, the insertion of anadditional refractory tube into the melting channel and the applicationof the unidirectional flow principle to a duplex induction furnaceconsisting, of a large capacity and a small capacity melting furnace.

:Patent application. Ser. No. 735,851, filed Mar...

20,, 1947, claims the creation of a unidirectional closed metal flowwithin the melting loop and the hearth of asingle induction furnace bythe connection of a refractory, current conductive tube with the meltingloop.

The. present application claims the application of the above recitedgeneral inventive idea of creating a-unidirectional metal flow by theinsertion of a refractory tube into a melting loop to an inductionfurnace having a plurality of chambers connected by this loop and thecreation of the closed metal flow through these chambers andthemeltingloop.

. Induction furnaces embodying the hitherto known metal movement in themelting channels and. the. one-way or unidirectional circulation of themelt in accordance with the invention will now be described in detailand with reference to the attached drawings.

;In the drawings,

Fig. 1 is a vertical section of the lower part of a submerged resistortype inductionfurnace illustratingv the customary metal. flow under theinfluence of the. pinch effect,

Figs. 2-5 illustrate the pressure conditions which prevail in. thisfurnace at the emergence of the melt from a melting channel into thehearth,

Fig.6 is a'vertical section of a double. chamber.

induction furnace online 66 of Fig. 7, equipped; to produce aunidirectional meta1 circulation. through both furnace chambersaccording to this invention,

Fig. 7: is a sectional view on line 1--! of Fig. 6, Figs. 8, 9 and 12-are vertical sectional views of further modifications of the tiltabledoublechamber furnaces shown in Figs. 6 and 7.

Fig. 10 is a vertical sectional view of a threechamber furnace on lineequipped in conformity with this invention,

Fig. 11 is a. sectional view of the same furnace on line l.l- |l of Fig.10,

Fig. 13 is a verticalsectional view of the furnace. similar to that ofFig. 6 showin a further modification.

The. furnace shown in Figs. 6 and 7 is equipped. with two metal holdingchambers or he'arths 1, 2.

l The secondary melting loop is located between these two chambers.

The loop consists of three melting channels 3, 4, 5 which connect thetwo chambers I, 2 and are threaded by primary transformer units composedof coils 6 of insulated copper wire and an iron core 1 which is closedtoward the coil windings.

The furnace is housed in casing B lined witha: refractory material 9,has a pouring opening I9, covers ii, closing plugs l2, and is tiltablysupported in bearings i9; customary means, such as electric hoists andhydraulic cylinders, will be- .provided to effectuate the tilting.

As apparent from the drawings, the melting channels 3, 4, 5 are paralleland equally inclined in such a manner thatstraight cleaning tools can beinserted through the openings'closed by plugs I2 into the channels whilethe same are full with the molten metal. Therefore the furnace can bekept in full operation during the cleaning of the melting channels; thisis true for the position shown in the drawings and for any tiltedposition of the furnace. In the hitherto known multichamber furnaces ofthis type the furnace had to be emptied for the insertion of thecleaningtools and the cleaning of the melting channels.

from the outside of the furnace could not be effected in the tiltedposition while the furnace was in operation and the melting channelswere kept full ofv the molten metal.

The means creating the homogenization of the metal in the two chambersI, 2 consist of a current conducting refractory, for instance, graphitetube 13 which, as illustrated in the drawings} is inserted into channel3; however, these tubes may be also inserted in the lateral channels,

whereby the metal circulation would be reversed insofar as the metalwill then flow from channels l, 5 into chamber 2, from there intochannel 3, then through chamber I and back into chan-- nels 4, 5.

The free end of tube [3 extends into a section of the metal bath held inchamber 2' which is practically free from the influence of theelectromagnetic field; the proper length of the tubewill vary inaccordance with the particular operating conditions of the furnace;however, that section of the hearth which is practically free of inducedcurrent and which therefore decides the length of the tube may beascertained without. difficulty as the extent of the electromagneticfield,

produced in these furnaces can be easily determined.

The upper or front portion of tube l3, which is 1 not under theinfluence of the electromagnetic field, is protected by a body of asuitable retrac l9--lll of Fig. 11

7 tory material, such as refractory brick l8, to prevent the breakage ofthe tube by the metal which is charged into the furnace chamber 2. Theportion of the tube directly adjacent to the transformer unit, however,remains unprotected and leaves the way open for the flow of the currentthrough the electrically conductive tube 13.

Due to the fluid pressure created by the induced electromagnetic fieldin channel 3 the metal is forced to flow from tube l3 in the directionof arrows [6; the outfiowing metal is replaced by metal flowing in thedirection of the arrows from chamber I into channel 3; accordingly metalmust flow from chamber 2 through channels 4, into chamber I and fromthere again into channel 3.

In this manner a steady continuous one or unidirectional circulation ofthe charge is produced through both chambers and a thoroughhomogenization achieved of the melts in the two chambers without theapplication of mechanical or furnace rocking means.

The tube 13 may extend, if desired, through the whole length of themelting channel as illustrated in Fig. 13.

In the modification of the invention shown in Fig. 8 the tube is soinserted into channel 3 that it extends into chamber I. The metal flowwill accordingly be reversed to that shown in Figs. 6 and 7. However,the unidirectional circulating and homogenizing action of tube I3remains unaltered.

In the furnace shown in Fig. 9 which otherwise is not different fromthose shown in Figs. 6-8 arcuated melting channes are provided which contrary to the furnaces of Figs. 6 and 8 could not be cleaned by straightcleaning tools during the operation of the furnace.

The furnace shown in Figs. 10 and 11 is a three chamber furnace which isequipped with metal holding chambers l, M, 2.

Two secondary melting loops are located between chambers l and I4 andbetween chambers 2 and I4. The loops consist as in the case of thepreviously described furnaces 8 to 9 of melting channels 3, 4, 5 whichconnect the metal holding chambers and are threaded by the primarytransformer units composed of coils S of insulated copper wire and ironcores 1.

The furnace is housed in a refractory lined casing 8, has covers H forthe three chambers and sealing plugs 12.

The means for creating the unidirectional metal circulation from thecenter chamber M into the lateral chambers l and 2 and the return flowinto center chamber 14 consist of the refractory cur m rent conductivetubes l3 inserted into the center channels 3.

The free ends of tubes l3 extend, as previously described, into asection of the metal bath which is substantially free from the influenceof the electromagnetic fields created by the inductor units. Therefractory protective brick I8 may also here be applied to tube l3 inthe previously described manner.

Due to the extension Of channels 3 by the tubes I3 the metal flows fromthese tubes into chambers I and 2, from there through channels 4, 5 intothe center chamber 14 and back into channels 3; thereby the samecontinuous unidirectional metal flow, as previously described, iscreated in a three chamber furnace.

As apparent from Fig. 12, the invention is here applied to adouble-chamber furnace where the melting channels are only accessible tothe introduction of cleaning tools after the charge has beenemptied-out; the furnace is otherwise equipped in the same manner as thefurnaces shown in Figs. 6 to 9.

As previously mentioned, the here described furnaces are particularlywell suited for the melting of metal scrap and also light metal scrap.The heat is generated at the bottom of the furnace and immediatelytransferred to the cold scrap from the melting channels by liquidcontact due to the continuous unidirectional metal flow. Therefore thefine metal particles are not subjected to high temperature from above.Hence the rate of oxidation before melting is reduced considerably. As afurther consequence of the unidirectional bath movement, the heattransfer and therefore the speed of melting is considerably increasedand any oxide formed is detached from the scrap particles and expelledto the surface of the bath.

1 claim:

1. In an induction furnace, a plurality of chambers located inspaced-apart relationship for holding molten metals, at least onesecondary loop composed of a plurality of melting channels connectingthe said chambers, at least one primary transformer unit threading saidsecondary melting loop adapted to create an electromagnetic field and tohold the metal in said chambers in the molten state, means for theproduction of a unidirectional closed circulation of the molten metalsbetween the said chambers through the melting loop, said means includinga refractory current conductive tube extending from a melting channelinto a chamber below the normal operating level of the metal andshifting the connection of said melting loop with said chamber into achamber section of reduced electromagnetic field intensity.

2. In an induction furnace, a plurality of chambers located inspaced-apart relationship for holding molten metals, at least onesecondary loop composed of a plurality of melting channels connectingthe said chambers, at least one primary transrormer unit threading saidsecondary melting loop adapted to create an electromagnetic field and tohold the metal in the said chambers in the molten state, means for theproduction of a unidirectional closed circulation of the molten metalsbetween the said chambers through the melting loop, said means includinga refractory current conductive tube extending from a melting channelinto a chamber below the normal operating level of the metal andshifting the connection of said melting loop and said chamber into achamber section which is free from the influence of the inducedelectromagnetic field.

3. In an induction furnace, a plurality of chambers located inspaced-apart relationship for holding molten metals, at least onesecondary loo composed of a plurality of melting channels connecting thesaid chambers, at least one primary transformer unit threading saidsecondary melting loop adapted to create an electromagnet field and tohold the metal in said chambers in the molten state, means for theproduction of a unidirectional closed circulation of the molten metalbetween the said chambers through the melting loop, said means includinga current conductive refractory tube connected with its one end to anoutlet of the loop into a chamber and terminating with the other endbeneath the normal operating level of the metal in a section of themetal holding chamber which is substantially'free from the influence ofthe .-.rilectmnnag netic field.

4. In an induction furnacaa pluralityof chambers located in spaced-apartrelationship for holding molten metals, at least one secondary ductiverefractory tube inserted with the oneend into a melting channel andterminating with the other end beneath thenormal operating level of themetal in a section of the metal holding chambar which issubstantially'free from the influence of the electromagnetic field.

5. In an induction furnace, two chambers located in spaced-apartrelationship for holding :molten metals, a secondary loop composed ofmelting channels connecting the bottom portion of the two chambers, atleast one primary transformer unit threading the said secondary meltingloop adapted to create an electromagnetic field and to hold the metal inthe two chambers in the molten state, means for the production of aunidirectional closed circulation of the molten metal between saidchambers through said melting 100p, said means including a clll'lflltconductive refractory tube connected with its one end to an outlet ofthe melting loop into a chamber and extending with the other end beneaththe normal operating level of the metal into a section of said chamberwhich is substantially free from the influence of the electromagneticfi'ld.

6. In an induction furnace, two chambers located in a spaced-apartrelationship for holding molten metals, the bottom of the said chambersbeing at different levels, a secondary loop composed of inclined meltingchannels connecting the bottom portion of the said two chambers, atleast one primary transformer unit threading the said secondary meltingloop adapted to create an electromagnetic field and to hold the metal inthe two chambers in the molten state, means for the production of aunidirectional closed circulation of the molten metal between saidchambers through said melting loop, said means including a currentconductive refractory tube connected with the one end to an outlet ofthe said melting loop into the chamber having its bottom at the higherlevel and extending with the other end beneath the normal operatinglevel of the metal into a siction of said chamber which is substantiallyfree from the influence of the electromagnetic field.

'7. In an induction furnace, two chambers located in a spaced-apartrelationship for holding molten metals, the bottom of the said chambersbeing at, different levels, a secondary loop compos:d of inclinedmelting channels connecting the bottom portion of the said two chambers,at least one primary tranformer unit threading the said secondarymelting loop adapted to create an electromagnetic field and to hold themetal in-the two chambers in the molten state, means for the productionof a unidirectional closed circulation of the molten metal between saidchambers through said melting loop, said means including a currentconductive refractory tube connected with the one end to an outlet ofthe melting loop into the chamber having its bottom at "the lower leveland extending with the other end beneath the normal operating level ofthe metal into a section of said chamber which is substantiallyfree'from the influence of the electromagnetic field.

-8. In an induction furnace, a center chamber and two lateral chambzrslocated in spaced-apart relationship for holding molten metals,secondary loops composed of a plurality of melting channels connectingthe said center chamber with the said lateral chambers, at least oneprimary transformer unit threading each of "the said secondary meltingloops adapted to create an electromagnetic field and to hold the metalin said chambers in the molten state, means for the production ofunidirectional closed flow s of the molten metal between the :center andthe lateral chambers through said melting loops said means includingcurrent conductive refractory tubes connected with the one end to anoutlet of the loops into a chamber and terminating with the other endbelow the normal operating level of the metal in a section of the metalholding chamber which is substantially free from the influence of theel:ctromagnetic field.

*9. In an induction furnace, a plurality of chambers located inspaced-apart relationship for holding molten metals, at least onesecondary loop composed of a plurality of melting channels connectingthe said chambers, at least one primary transformer unit threading saidsecondary melting loop adapted to create an electromagnetic field and tohold the metal in said chambers in the molten state, means for theproduction of a unidirectional closed circulation of the molten metalbetween said chambers through melting loop, said means including acurrent conductive refractory tube connected with its one end to anoutlet of the loop into a chamber and terminating with the other endbeneath the normal operating level of the metal in a section of themetal holding chamber which is substantially free from the influence ofthe electromagnetic field and a refractory metal resistant protectivebody applied to the said tube on a major portion of its length extendingin a metal holding chamber.

10. In an induction furnace, a plurality of chambers located inspaced-apart relationship, for holding molten metals, at least onesecondary loop composed of a plurality of melting channels connectingthe said chambers, at least one primary transformer unit threading saidsecondary melting loop adapted to create an electromagnetic field and tohold the metal in said chambers in the molten state, means for theproduction of a unidirectional closed circulation of the molten metalbetween said chambers through melting loop, said means including agraphite tube connected with its one end to an outlet of the loop into achamber and terminating with the other end beneath the normal operatinglevel of the metal in a section of the metal holding chamber which issubstantially free from the influence of the electromagnetic field.

11. In an induction furnace, a plurality of chambers located inspaced-apart relationship, for holding molten metals, at least onesecondary loop composed of a plurality of melting channels connectingthe said chambers, at least one primary transformer unit threading saidsecondary melting loop adapted to create an electromagnetic field and tohold the metal in said chambers in the molten state, means for theproduction of a unidirectional closed circulation of ten metal.

the molten metal between said chambers through melting loop, said meansincluding a carborundum tube connected with its one end to an outlet ofthe loop into a chamber and terminating with the other end beneath thenormal operating level of the metal in a section of the metal holdingchamber which is substantially free from the influence of theelectromagnetic field.

12. A method of producing homogeneous metal melts in multi-chamberinduction furnaces which are provided with a secondary loop composed ofmelting channels connecting the chambers and with at least onetransformer unit threading said loop and adapted to create anelectromagnetic field, comprising holding by means of the said field ametal charge in the said chambers in a molten state, advancing theoutflow of the metal from a melting channel into a section of a metalholding chamber which is substantially free from the influence of thesaid electromagnetic field, creating a continuous unidirectional flow ofthe metal through the said chambers and the said melting loop andobtaining hereby complete homogenization of the mol- MARIO TAMA.

12 REFERENCES crrnn The following references are of record in the fileof this patent:

5 UNITED STATES PATENTS Number Name Date Re. 22,602 Tama Feb. 13, 19451,312,069 Wyatt Aug. 5, 1919 1,660,407 Bainbridge Feb. 28, 1928 101,792,449 Spencer Feb. 10, 1931 1,793,137 Russ Feb. 17, 1931 1,944,855Wadman Jan. 23, 1934 2,339,964 Tama Jan. 25, 1944 2,375,049 Tama May 1,1945 15 2,381,523 Tama et a1. Aug. 7, 1945 2,386,369 Thompson Oct. 9,1945 2,397,785 Friedlander Apr. 2, 1946 FOREIGN PATENTS 20 NumberCountry Date 126,947 Great Britain Dec. 24, 1919 142,110 Great BritainApr. 20, 1920 788,006 France July 22, 1935

